Clearly Jose Mourinho shrewdly spent last season contemplating and building his longer term strategy. He knew that it would take some mediocre performances last season (individual and team) to see where the gaps were. The club were always going to allow him time to do this, so the UEFA and League Cup wins were nice bonuses,

As a result of this pre planning, Mourinho knew exactly which players he wanted to buy in the transfer window and completed all his deals long before the closing day, unlike Chelsea for example, who were still scrabbling about up to the last minute. No wonder Mourinho has called for the transfer window to close before the start of the Premier League season, (https://www.worldfootball.net/teams/manchester-united/2018/6/)

The Manchester United manager looks comfortable and confident at the moment, not only because of the results but because clearly the performances and effectiveness of his tactics are going exactly to plan,

We haven’t actually seen Jose looking this happy for a while. The petulant tantrums that came to be the norm at both Chelsea and United from the latter part of 2015 through the end of last season have even given way even to a bit of fun https://www.youtube.com/watch?v=AoRFcN0-Yj4